title: Improved recovery of the hemodynamic response in diffuse optical imaging using short optode separations and state-space modeling.
abstract: Diffuse optical imaging (DOI) allows the recovery of the hemodynamic response associated with evoked brain activity. The signal is contaminated with systemic physiological interference which occurs in the superficial layers of the head as well as in the brain tissue. The back-reflection geometry of the measurement makes the DOI signal strongly contaminated by systemic interference occurring in the superficial layers. A recent development has been the use of signals from small source-detector separation (1cm) optodes as regressors. Since those additional measurements are mainly sensitive to superficial layers in adult humans, they help in removing the systemic interference present in longer separation measurements (3 cm). Encouraged by those findings, we developed a dynamic estimation procedure to remove global interference using small optode separations and to estimate simultaneously the hemodynamic response. The algorithm was tested by recovering a simulated synthetic hemodynamic response added over baseline DOI data acquired from 6 human subjects at rest. The performance of the algorithm was quantified by the Pearson R(2) coefficient and the mean square error (MSE) between the recovered and the simulated hemodynamic responses. Our dynamic estimator was also compared with a static estimator and the traditional adaptive filtering method. We observed a significant improvement (two-tailed paired t-test, p<0.05) in both HbO and HbR recovery using our Kalman filter dynamic estimator compared to the traditional adaptive filter, the static estimator and the standard GLM technique.
authors.affiliation: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Charlestown, MA, USA. lgagnon@nmr.mgh.harvard.edu
authors.forename: Louis
authors.initials: L
authors.lastname: Gagnon
authors.forename: Katherine
authors.initials: K
authors.lastname: Perdue
authors.forename: Douglas N
authors.initials: DN
authors.lastname: Greve
authors.forename: Daniel
authors.initials: D
authors.lastname: Goldenholz
authors.forename: Gayatri
authors.initials: G
authors.lastname: Kaskhedikar
authors.forename: David A
authors.initials: DA
authors.lastname: Boas
mesh_terms: D000328:Adult; D000465:Algorithms; D001696:Biomechanical Phenomena; D001921:Brain / Q000033:anatomy & histology* / Q000502:physiology; D002560:Cerebrovascular Circulation / Q000502:physiology*; D003952:Diagnostic Imaging / Q000379:methods*; D006439:Hemodynamics / Q000502:physiology*; D006454:Hemoglobins / Q000032:analysis / Q000378:metabolism; D006801:Humans; D007091:Image Processing, Computer-Assisted; D016018:Least-Squares Analysis; D016014:Linear Models; D008279:Magnetic Resonance Imaging; D015233:Models, Statistical; D016011:Normal Distribution; D010100:Oxygen / Q000097:blood; D019265:Spectroscopy, Near-Infrared
chemical_list: D006454:Hemoglobins; D010100:Oxygen